I sandblasted the inside of my tank. It worked pretty good from what I could see, and my fuel filter has been clean ever since. The only downside is getting the sand out. I had to run compressed air through it for about an hour! Then, I rinsed it out with gas a few times. I tried acid, but the stuff I got was too weak. I used "Lime Away" and it didn't do anything. I couldn't find any Phosphoric acid and I heard that muriatic acid requires a coating after using because it's so corrosive and will start rusting right away if you don't paint it or keep the tank full of gas all the time.
If you sandblast the tank, you should use a fuel filter (well, you should use a fuel filter no matter what).